Evaporator defrosting arrangement



Feb. 19, 1957 L. B. M. BUCHANAN EVAPORATOR DEFROSTING ARRANGEMENT Filed Dec. 11, 1953 3 Sheets-Sheet 1 INVENTOR LESLIE B.M.BUCHANAN ATTORNEY Feb. 19, 1957 L. B. M. BUCHANAN 46 EVAPORATOR DEFROSTING ARRANGEMENT Filed Dec. 11, 1953 3 Sheets-Sheet 2 INVENTOR LESLIE B.M. BUCHANAN ATTORNEY Feb. 19, 1957 B. M. BUCHANAN EVAPORATOR DEF'ROSTING ARRANGEMENT 3 Sheets-Sheet 3 Filed Dec. 11, 1953 F l G 5 INVENTOR LESLIE B.M. BUCHANAN ATTORNEY 2,781,646 EvAroRAToR DEFROSTING ARRANGEMENT Leslie R. M. Buchanan, Wilbraham, Mass., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pin, a corporation of Pennsylvania Application December 11, 1953, Serial No. 397,530 4 Claims. (Cl. 62-126) This invention relates to refrigerating apparatus and more particularly to means for defrosting the evaporator or cooling unit of a domestic refrigerator.

It is the principal object of my invention to rapidly defrost the refrigerant evaporator of a domestic refrigorator.

It is another object of my invention to effect defrosting in such a manner as to prevent the melting of frozen food stored within the evaporator.

In Patent No. 2,459,173, granted January 18, 1949, to G. S. McCloy and assigned to the assigneee of my invention, there is disclosed a system and method for defrosting refrigerant evaporators by means of heated refrigerant gas. Generally, this system consists of a conventional compressor-condenser-evaporator refrigerating circuit modified by the addition of a heater for heating the refrigerant entering the evaporator to effect defrosting, and a storage vessel adapted to store liquid refrigerant during a cooling cycle and discharge this stored refrigerant into the evaporator during defrosting. During a defrosting cycle of this system, the heater vaporizes the major portion of the refrigerant flowing to the evaporator, which then condenses within the evaporator, giving up heat to melt frost. The condensed refrigerant returning to the compressor is reevaporated by heat from the hot gas leaving the compressor. For moderate size evaporators this system performs satisfactorily. However, with larger size evaporators, that is, evaporators having a large refrigerant capacity, in order to raise the temperature of the exit end of the evaporator to above freezing in a short period of time, it is necessary to heat the gas entering the evaporator to an undesirably high temperature. The result is that the inlet portion of the evaporator may be warmed to as high as 150 F. before the exit portion of the evaporator is free of frost. High temperatures such as these, even for very short periods, are detrimental to frozen foods which are stored on or within the evaporator.

It is therefore an object of my invention to utilize a so-called hot gas defrosting system for defrosting evaporators of a size larger than those heretofore defrosted by this method without raising the temperature of any portion of the evaporator excessively.

With my improved defrosting apparatus only enough heat is applied to the refrigerant entering the evaporator to insure that all of the refrigerant is vaporized. As this gaseous refrigerant passes through the cold refri erant passages it condenses, giving up its heat of condensation to melt frost from the evaporator. At a point intermediate the inlet and outlet of the evaporator where sufficient heat has been taken from the refrigerant to convert most of it back to a liquid, heat is again applied to convert the liquid back to a gas. While one reheating should be sufficient to effectively defrost most conventional evaporators without raising the temperature of the gas to an undesirably high value, it would of course be possible, in accordance with the principles of my in vention, to continue reheating the refrigerant at intervals nited States Patent throughout the passages of unusually large evaporators.

These and other objects are effected by my invention as will be apparent from the following description taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. l is a schematic drawing of a refrigerating system embodying my invention;

Fig. 2 is a perspective view of the rear of a refrigerant evaporator embodying my invention;

Fig. 3 is a phantom view of the evaporator shown in Fig. 2 and showing the refrigerant passages around the sides, top and bottom of this unit;

Fig. 4 is an enlarged view of a portion of the evaporator shown in Fig. 2 and showing the defrost heat exchanger of my invention; and

Fig. 5 is an enlarged cross sectional view of the heat exchanger, taken along the line V-V of Fig. 4.

Referring to the drawings and more particularly to Fig. 1, it will be seen that my invention utilizes the 'elements of a conventional, mechanical refrigerating system including a compressor It), a condenser 11 and a cooling unit or evaporator 12. Hot gaseous refrigerant compressed by the compressor 10 is conveyed by a hot gas line 13 to the condenser 11, where it is cooled and converted to a liquid. Liquid refrigerant leaving the condenser 11 passes through a liquid line 14 including a restrictor or capillary tube to the inlet 16 of the evaporator 12. The refrigerant vaporizes in the evaporator 12, absorbing heat from the evaporator structure and the surrounding air. This gaseous refrigferant then flows from the evaporator outlet 17 through a suction line 13 and back to the compressor 10, where the gas is compressed and the refrigeration cycle repeated.

It is to be understood that the evaporator or cooling unit 12 is generally positioned within an insulated chamber (not shown) suitable for the storage of foodstuffs. Generally, the space within the evaporator structure is maintained at a temperature below freezing and, therefore, suitable for the storage of frozen food, ice trays and the like.

The temperature of the evaporator 12 is maintained substantially constant by cycling the compressor 10 be tween on and off. A conventional control for this purpose is shown in Fig. 1 and consists generally of a thermostatic switch 19 responsive to evaporator temperature and controlling energization of the compressor 1%) from electrical supply lines 20. Inasmuch as the construction and operation of such control arrangements are well understood by those skilled in the art, no detailed description thereof is deemed necessary here.

The refrigerating circuit of Fig. l utilizes the conventional heat exchanger between the liquid line 14 and the suction line 18 as indicated at 21. My improved circuit also utilizes a second heat exchanger between the suction line 18 and the hot gas line 13 as indicated at 22. The function of this latter heat exchanger will be explained more fully hereinafter.

In a preferred form of my invention, the evaporator 12 is of box-like construction with the sides, top and bottom of the unit formed of a single wrap-around metal sheet 23 and the rear Wall formed of a pair of metal sheets 24. The front of the evaporator is open to provide access to its interior frozen storage area. As best illustrated in Fig. 2 of the drawings, the refrigerant passages adjacent the inlet in and the outlet 1.7 are formed between the evaporator back sheets 24. The intermediaterefrigerant passage 26 is formed by a tube wrapped in serpentine fashion about sheet 23 and communicating at 27 and 28 with the refrigerant passages within sheets 24. The tube forming passage 26 is preferably fastened in good heat exchange relationship with the sheet 23, as by brazing.

Referring specifically to the construction of the refrigerant passages shown in Figs. 4 and 5, it will be noted that a portion 29 of the passage adjacent the evaporator inlet 16 is formed between the sheets 24 in a manner to provide a recess 31 for the reception of a sheathed electric heating element 32. The heater 32, when energized, serves to heat refrigerant flowing through passage 29, as will be more fully explained hereinafter. The passage 29 communicates with a storage vessel 33 likewise formed by and between sheets 24. The storage vessel 33 is provided with a pair of outlet passages 34 and 36 communicating respectively, with upper and lower portions of the vessel 33. The upper passage 34 is crimped or other wise restricted at 37 and communicateswith the other outlet passage 36, which is provided with an elevated portion 38 between its connection to the vessel 33 and its connection to the passage 34. The storage vessel 33 and passages 34 and 36 make up a refrigerant liquid trapping and releasing system of the type disclosed and claimed in U. S. Patent No. 2,459,173 to G. S. McCloy and reference is herein made to that patent for a more detailed description of the operation of the system.

Refrigerant passage 36 communicates with the tubular refrigerant passage 26 at 27 and this passage is in turn connected to an accumulator 39 formed by and between sheets 24. The accumulator 39 is connected to the suction line 18 by an outlet passage 41.

The intermediate refrigerant passage 26 is provided with a loop 42 approximately mid-way between its ends 27 and 28. This loop 42 is not attached to sheet 23 but instead extends around the rear of back plates 24. A portion 43 of the loop 42 is formed to a kidney shaped cross section and held in contact with the heating element 32 by means of a clamp 44.

Heating element 32 is energized from supply lines 21 under joint control of a defrost energization switch 46 and thermostatic switch 19. Defrost switch 46 may be closed manually to initiate defrosting or may be actuated automatically by a mechanism of the type disclosed in Patent No. 2,595,967 granted May 6, 1952, to G. S. McCloy and assigned to the assignee of this invention. This patent discloses and claims a mechanism for counting the door openings of a refrigerator and for closing a defrost switch after a predetermined number of openings. It is to be understood, however, that other means, such as, for example, a clock, may be used for closing switch 46 automatically to initiate defrosting.

Operation With the heater 32 deenergized, the apparatus of this invention functions much in the same manner as a conventional mechanical refrigerating system. The refrigerant compressed by the compressor 19 and condensed in condenser 11 passes through the capillary tube liquid line 14 into the evaporator or low pressure side of the system. Liquid refrigerant, plus a small amount of so'called flash gas, which has formed in the capillary tube 14, enters the refrigerant passages of the evaporator at the inlet 16, flows through passage 29 and into the storage vessel 33. Gaseous refrigerant is released from the storage vessel 33 through the restrictor 37 and outlet passage 34 while the liquid portion of the refrigerant collects within storage vessel 33 until it is filled. The restrictor 37 is large enough to permit sufl'icient liquid and gaseous refrigerant to flow into the remainder of the refrigerant passages of the evaporator to effectively cool the evaporator. The raised portion 38 of outlet tube 36 prevents liquid refrigerant from escaping from the storage vessel 33 so long as the pressure drop across restrictor 37 is less than the head of liquid within the raised portion 38. The refrigerant continues to flow through intermediate refrigerant pa-ssage 26, wherein it evaporates and absorbs heat from the evaporator and the surrounding air. The gaseous refrigerant is separated from the remaining liquid in the accumulator 39 and is withdrawn through suction line 18 and returned to the compressor 10. The cold low pressure gas flowing through suction line 18 cools the capillary tube 14 through the heat exchanger 21 and minimizes the vaporization of refrigerant within the capillary tube.

The frost which collects on the evaporator structure during refrigeration requires periodic removal which is accomplished by closing switch 46 to energize defrost heater 32. It will be noted that defrost heater 32 is controlled jointly by switch 46 and the thermostatic control switch 19 for the compressor 10. Therefore, heater 32 is energized only when compressor 10 is operating and refrigerant is being circulated through the circuit.

With the heater 32 energized, heat is applied to the liquid refrigerant flowing through refrigerant passage 29. The major portion of the refrigerant flowing through passage 29 is therefore converted to a gas which passes into the storage vessel 33 in such quantity as to not readily pass through the restrictor 37. The pressure within storage vessel 33 is, therefore, increased, driving the liquid refrigerant stored therein out through outlet passage 36 and into intermediate refrigerant passage 26. The storage vessel 33 contains a sufiicient quantity of refrigerant liquid to flood the remaining refrigerant passages of the evaporator 12 and to cause liquid refrigerant to spill over into the suction line 18. A portion of this liquid refrigerant is vaporized in heat exchanger 21, a major portion of the liquid is vaporized by heat from the hot gas line 13 through heat exchanger 22 and any remaining liquid refrigerant that spills into the compressor 10 is vaporized within the compressor casing. This vaporization of refrigerant within the suction line 18 raises the pressure within the evaporator 12, preventing the vaporization of refrigerant within the evaporator, and stopping the refrigerating process.

The refrigerant vaporized by the heater 32 now begins to condense within the evaporator refrigerant passages, giving off heat to melt the frost from the evaporator. in accordance with my invention, I prefer to add only enough heat to passage 29 to vaporize, but not superheat, the

' refrigerant flowing therethrough. With the pressure existslightly above 32 F.

ing with the evaporator due to vaporization of refrigerant within the suction line 18, all of the refrigerant flowing through passage 29 will be vaporized when heated to In large size evaporators, the refrigerant flowing through passage 26 will recondense before reaching evaporator outlet 17.

This liquid refrigerant is reheated and revaporized within loop 42 of the refrigerant passage 26, which is arranged in heat-exchange relationship with the heating element 32. This heat exchanger is likewise proportioned to heat the refrigerant flowing therethrough only sufficiently to vaporize the refrigerant without superheating it. The vaporized refrigerant leaving loop 42 passes through 3 the remainder of refrigerant passage 26, wherein it condenses, giving up heat to melt the frost from the remainder of the evaporator.

Suitable means may be provided for deenergizing the heater 32 when all the frost has been removed from the evaporator 12.

It can thus be seen that by heating and reheating the refrigerant flowing through the evaporator during a defrosting cycle, at no point in the circuit is the refrigerant heated to an undesirably high temperature, and yet all portions of the evaporator are quickly and effectively defrosted. It is to be understood that, in place of the single heater 32 employed in the preferred embodiment of my invention, two heaters could be used, each of a lower wattage, with one applying heat to the refrigerant passage 29 and the other applying heat to the loop 42 which. in this case, need not necessarily be placed on the back wall of the evaporator.

It will also be noted that there is a counter-flow relationship between the refrigerant passing through passage 29 and refrigerant passing through tube 42 in the perferred embodiment of my invention. This arrangement ensures an even transfer of heat from the heater 32 and prevents any portion thereof from becoming overheated. From the foregoing, it will be apparent that I have devised a novel and effective arrangement for refrigerating and defrosting the evaporator of a mechanical refrigerating system.

While I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof.

What is claimed is:

1. An evaporator having a refrigerant passage including an inlet and an outlet and means for defrosting said evaporator by the application of heat to but portions of said refrigerant passage, which portions constitute substantially less than the total length of refrigerant passage for said evaporator, and by the circulation of heated refrigerant within said evaporator passage, said evaporator passage having a first portion adjacent the inlet thereof adapted to have refrigerant vaporized therein during defrosting, said evaporator passage having a second portion thereof adapted to have refrigerant condensed therein during defrosting, said evaporator passage having a third portion thereof adapted to have refrigerant vaporized therein during defrosting, and a fourth portion of said evaporator passage adapted to condense refrigerant therein during defrosting, said evaporator passage portions being serially connected in the order named, and means for heating said first and third passage portions for defrosting said evaporator, said second and fourth passage portions being heated by the condensation therein of refrigerant fluid vaporized in said first and third passage portions.

2. An evaporator provided with a refrigerant passage having an inlet and an outlet, and means for defrosting said evaporator by the application of heat to but portions of said refrigerant passage, which portions constitute substantially less than the total length of the refrigerant passage, and by the circulation of heated refrigerant within said evaporator passage, said evaporator passage having two portions thereof arranged in closely spaced'relationship, one of said portions being adjacent the inlet of the evaporator passage and the other of said portions being intermediate the inlet and outlet of the evaporator passage and being downstream of said first portion a distance sufficient to receive refrigerant which has previousiv been evaporated in said first passage portion and recondensed in a third portion of the passage intermediate said first and second portions, said heat applying means comprising a single heater disposed in heat-exchange relationship with both said first and second portions of the evaporator passage.

3. In an evaporator structure for refrigerators, the combination of a refrigerant passage having an inlet and an outlet and comprising first, second, third and fourth portions serially arranged between the inlet and outlet thereof, and means for applying heat to the first and third portions of said passage for the vaporization of refrigerant therein, said second and fourth evaporator portions being spaced from said heating means and deriving heat for the defrosting thereof from the condensation therein of refrigerant vaporized in said first and third passage portions, whereby said entire evaporator structure may be defrosted by the application of heat to but the first and third passage portions.

4. The combination as set forth in claim 3 and further characterized by having the said first and third passage portions arranged in closely spaced relation and a single heater for applying heat to said first and third passage portions.

References Cited in the file of this patent UNITED STATES PATENTS 2,492,397 Peterson Dec. 27, 1949 2,511,419 Smith June 13, 1950 2,661,602 Lanker Dec. 8, 1953 2,665,567 King et al Jan. 12, 1954 

